This invention relates to systems and apparatuses designed for water treatment. More specifically, the invention relates to water treating equipment in which coalescence and flotation can occur within a single treatment vessel.
Selection of water treating equipment is typically based on inlet conditions, outlet specifications required, and operating conditions such as temperature and chemical used for the treatment. Inlet conditions include oil droplet size and concentration; inlet fluid physical and chemical properties such as API gravity of oil and salinity of produced water; and the type of chemical and dosage used for the treatment.
Outlet specifications required depend on whether onshore or offshore discharge or reinjection is involved. For offshore discharge, the outlet specification, which can vary by location and country, is typically about 29 ppm of oil-in-water for the Gulf of Mexico. For reinjection, the outlet specification can depend on such factors as the type of reservoir involved (e.g. a tight formation or not). Typically, the outlet oil and solid specifications are less than 5 ppm.
For an offshore discharge application to meet the 29 ppm specification, a liquid/liquid hydrocyclone unit followed by a flotation unit is the preferred process flow scheme. The hydrocyclone unit is typically compact to reduce space and weight requirements.
For an onshore discharge or reinjection application to meet the less than 5 ppm specification, a skimmer followed by a corrugated plate interceptor (“CPI”) followed by flotation unit and nutshell filter unit is the preferred process flow scheme. Because the largest CPI can only process up 60,000 barrels/day of fluid, a large throughput facility (e.g., greater than 240,000 barrels/day) would require at least four trains to process that throughput.